One of the pervasive features of consumer audio and video electronic components in recent years has been and continues to be the handheld remote control. The handheld remote control sends control signals to the controlled device by irradiating the device with infrared energy generated by infrared photo emitter diodes. The controlled device receives a pattern of intermittent irradiation or illumination comprising a control signal.
The remote control unit has stored patterns corresponding to push buttons assigned to various functions of the controlled device. Activating a button causes the excitation of the photo emitter diode according to the stored pattern, thereby generating and transmitting a control signal. Control signals tend to be short words of data representing a low order numeric signal corresponding to some function of the controlled electronic appliance. Conventionally, infrared (IR) remote control units use a carrier frequency of between 10 kHz and 75 kHz. The controlled device receives the signal with a photo detection diode and circuitry that interprets as logical lows and highs the alternating illumination of the photo emitter diode on the remote control unit. Such a signal corresponds to the pattern stored in the remote control unit.
Various manufacturers have selected unique numeric codes to control their devices. This unique coding has allowed differentiation between such devices. For instance, a Brand X VCR will have a limited vocabulary of signals that influence its action. The Brand Y television will have a different limited vocabulary of signals. If a signal is not present within a device's vocabulary, the device will do nothing. With several devices, each having a distinct and limited vocabulary, a single universal remote control can control all of them, distinctly.
While infrared transmission of control signals is an inexpensive and reliable means of controlling one or more devices, it suffers from several shortcomings. The remote control unit transmits much as a flashlight illuminates. All transmissions propagate strictly along lines of sight. If walls, enclosures, furniture, or people block the path between the remote control unit and the controlled device, the controlled signal is occluded and the device cannot respond. A VCR in a cabinet enclosure will not respond.
Further, as in an auditorium or restaurant, if several of the same brand and model of device are present, a single signal might affect a plurality of those devices present. As only those of the units that the remote control unit illuminates by the emission of its photo emitter diode will receive the signal, the number of units that respond may not always be uniform or predictable.
In U.S. Pat. No. 4,809,359, issued Feb. 28, 1989, and U.S. Pat. No. 5,142,397, issued Aug. 25, 1992, the inventor Dockery teaches a system for extending the range of an infrared remote control system. The system comprises two units known as repeaters. The first repeater receives the infrared control signal from the handheld remote control unit and translates that signal to a corresponding UHF radio frequency signal. The second repeater, located remotely from the first and adjacent to the controlled device, receives the UHF signal and reconstitutes it into an infrared control signal equal to that the handheld remote control unit sent to the first repeater. The controlled device then receives it and responds just as it would to the handheld remote control unit.
The advantage to the Dockery system is that it teaches a signal that will pass through obstructions. The handheld remote control and first repeater of the Dockery patent can control a VCR and second repeater entirely enclosed within a cabinet or even in a second room. Such a system of repeaters allows for a home entertainment system that is inconspicuous within a room or a centrally wired programming center that is remote from the television unit.
The Dockery teaching has several disadvantages however. Principal among those disadvantages is the lack of selectivity. The infrared remote control device will transmit only within a single room and within that room only to those devices illuminated by the photo emitter diode. The first repeater in Dockery's patent, on the other hand, will transmit through walls and other structures. In a home, apartment building, or other area with multiple repeater sets present, one first repeater can be in signal communication with several of the second repeater units. This “crosstalk” between signal units may result in the unintended control of several controlled devices, especially devices outside of the presence of the viewer or listener.